When compressed natural gas or compressed hydrogen gas is stored in cylinders at pressure as high as 6,000 psig, without equipped a fuel pump, an electrical solenoid is used to control fuel flow to quickly start and stop the fueling process. There exist some problems in the current electrically operated pilot-type, “instant-on” solenoid valves, especially during the opening and closing stage of the valve. In the prior arts U.S. Pat. No. 5,762,087 and No. 6,540,204; a ring segregates the primary piston to form a front side and a back side, where the front side is in the direction of the outlet. When the solenoid is energized, a pressure difference is created between the front side and the back side and it overcomes the biasing elements to open the solenoid valve. During the opening process, a small ratio of the amount of gas of inlet to outlet of the back side of the primary piston is desired, because it helps to open the valve. However, in this case, such ratio is rather critical and it can not be easily determined. During the valve close procedure, as the pilot piston is trying to adjust itself to a seal position, the amount of gas leaking from the back side of the primary piston to the outlet of the valve may be higher than that of supplying from the front side. Hence, the pressure won't be able to build up in the back side. Under this circumstance, because the spring force can not overcome the pressure difference between the back side and the front side of the primary piston, the valve might not close eventually.
In this invention, two matching surfaces between the primary piston assembly and valve body chamber is designed in such a way that the gas flow is restrained from the front side to back side of the primary piston assembly to create a pressure difference when the solenoid energizes, so that the valve open instantly. A channel hole is introduced to maintain the pressure difference between the front side and the back side of the primary piston assembly while when the valve opens. Unlike the prior arts, during the closing process and when the pilot piston adjusts itself to a seal position, the amount of gas entering the back side of the primary piston assembly is faster than the amount of gas leaking and that since a certain pressure difference is maintained, the valve can be closed quickly. In either case, the ratio of the amount of gas is not critical.
Another feature disclosed in the present invention is that an axial center column mounting in the housing of the valve provides a bleed hole seat and an axial passage being in communication fluid with the outlet chamber. The magnetic field generated by the permissible electrical power of the solenoid will determine the maximum travel stroke of the pilot piston. In this invention, since the pilot piston does not sit on the primary piston assembly, the stroke of the primary piston is not limited under such permissible condition.